Human cells have developed many mechanisms to inhibit viral replication, and viruses have evolved diverse strategies to resist their effects. This balance between the virus and its host is exemplified by the anti-HIV properties of the APOBEC family of cytidine deaminases and the HIV-encoded regulatory protein, Vif. Cultured cell experiments have shown that at least three APOBEC proteins, APOBEC3G (hA3G), APOBEC3F (hA3F), and APOBEC3B (hA3B) can profoundly inhibit HIV infection. Viral suppression is mediated through both DNA editing-dependent (i.e., C-to-U deamination of nascent first strand reverse transcripts that is manifested as G-to-A mutation of the coding strand) and/or -independent (i.e., prevention of reverse transcript accumulation) mechanisms. The protective role of HIV Vif is exerted through bridging an interaction between hA3G/F and a cullin5-SCF-like E3 ubiquitin ligase such that the hA3G/F proteins are degraded in virus-producing cells. Thus, the dynamic between hA3G/F and HIV Vif might be a critical determinant of HIV transmission as well as the outcome of infection. Recent work has allowed insights into the relative importance of these factors. Nevertheless, the reported associations between hA3G gene expression and DNA polymorphism in the coding region and progression to AIDS after infection are complex and contradictory. These conflicting findings suggest that the effects of these innate host factors have not been investigated adequately. The overall goal of this proposal is to achieve a fundamental understanding of the HIV Vif/hA3G/F/B conflict and its influence on susceptibility and resistance to infection and the rate of progression to AIDS. We will measure hA3G/F/B gene expression (both mRNA and protein) in phenotypically defined cell populations, localize their expression in cell subsets in tissue, and examine genetic variability (DNA polymorphisms) and their genetic and haplotype associations that influence susceptibility and resistance HIV infection and progression to AIDS. We will perform this work with the information and clinical samples obtained from individuals enrolled in natural history cohort studies (i.e., the MACS and WIHS). We will use rigorous statistical methods to prove (or disprove) correlations between experimental measurements (i.e., the abundance of gene expression [both mRNA and protein] by cells of defined phenotype and location, the extent of G-to-A hypermutation, viral sequence diversification, and variation in the v/fand hA3G/F/B genes and proteins) and HIV pathogenesis. This newfound knowledge of how the Vif/hA3G/F/B conflict affects HIV infection should prove useful in the search for new drug treatments that leverage the activity of this innate antiviral defense mechanism.